Prodecural ring texture
After you answer in the comments, here's a simple setup:

The square root of the dot product is the distance to the center (in this case, the distance to an empty object).
Adding some value to it before the module operation will just make the colors to cycle.
Scaling the rings loop is also possible by multiplying the distance with some other value, before the add node. Values less than 1 will produce wider rings, and values bigger than 1, thinner rings.